Challenges and emerging solutions
Agriculture is faced with an urgent need to evolve in response to the
global challenges of the 21 century. The recently released IPCC climate
report indicates a faster progression of climate change than previously
expected. Climate models predict severe impacts for agriculture on a
global level. In Europe, severe impact on yield due to temperature
increase and changes in precipitation is imminent [1]. Globally
major impacts of soil erosion in tropical regions will reduce the
farmable area [2]. Currently classical breeding for spring wheat can
barely mitigate the existing yield affecting factors, and the situation
is projected to get worse [1]. Looking into other aspects
agriculture needs to battle, like the impact of pests, biodiversity,
soil depletion and extensive fertilizer and chemical use, it is evident
that a second green revolution of agriculture and plant breeding is
urgently needed.
The advent of site-specific nuclease (SSN) based genome editing
technologies have resulted in a great interest in their applications in
plant breeding. Much emphasis has been placed on the ability of genome
editing technologies to introduce beneficial mutations in an elite
genetic background without the high number of background mutations or
linkage drag associated with conventional approaches. However, this
‘precision breeding’ strategy has limitations 1) it requires knowledge
about the identity and function of the target gene and 2) it only
applies to traits which can be modified through one or a few genes. A
different strategy is clearly in need for exploiting the full diversity
of adaption found in nature. We propose that the answer may lie in
turning the concept of precision breeding upside down. Rather than
attempting to first understand and then re-engineer the complex genetic
networks that confer environmental adaptation to wild plants, it may be
more feasible to acquire these networks for agriculture by domesticating
the wild plant itself.
The major stable crops of the modern world were domesticated in
prehistoric times and perfected over millennia. Although there are some
examples of modern domestication like blueberries, blackberries or
strawberries, these novelty crops do not compete directly with the
staples [3-5]. It is undoubtedly a bold proposal to re- or de
novo - domesticate staple crops. However, we do so because we see the
synergy of progress in two areas. Genome editing technology and
molecular characterization of the genes behind the domestication
syndrome in major crops. Thus, it should be feasible to accomplish or
repeat domestication by the application of genome editing to wild plants
by using already domesticated relatives as a roadmap. We propose to call
that approach “G enome E diting a cceleratedRe -D omestication” (GEaReD ) (see Fig. 1).
GEaReD rely on the natural selection happened over millions of years to
secure adaptation and resilience. Agronomic and possibly food safety
traits are then introduced with techniques such as CRISPR/Cas9,
CRISPR/Cas9 Integrase/Isomerase or PRIME-CRISPR to create highly adapted
plants with yield and quality that can compete with current cultivars
(see Fig. 1). Since Genome Editing can accelerate breeding
substantially, it would be possible to generate new cultivars in 2-4
years compared to the current much longer timeframe. The road tode novo domestication of wild plants for new breeding material or
even new cultivars has never been shorter. The first examples include
the de novo domestication of a ground cherry (Physalis
pruinosa ) and wild tomatoes [6, 7]. These first reports were
shortly followed by reports on cereal de novo domestication.
Recently work on African rice landraces, and their ability to accelerate
domestication and development by CRISPR-mediated genome editing was
published [8]. Furthermore, a roadmap including the necessary tools
and examples of their application for the domestication of
allotetraploid rice has been provided [9].